The present invention relates to a vacuum cleaner having a silencer mechanism and, more particularly, to a vacuum cleaner having a resistance type silencer mechanism provided on a vacuum cleaner main body for flowing an exhaust air from an electric driven blower at an outside portion.
A conventional vacuum cleaner having a silencer mechanism is disclosed in, for example, Japanese Utility Model Laid-Open No. 115853/1987, wherein a vacuum cleaner main body of the vacuum cleaner provides a sound absorption box which is positioned between an electric driven blower receiving chamber and a cord winding apparatus receiving chamber. The sound absorption box has an intake port and a plurality of exhaust air ports.
As a result, a resonance type silencer mechanism for the vacuum cleaner main body is provided which is constituted between an outer peripheral surface portion of the sound absorption box and an inner wall portion of the vacuum cleaner main body.
Another construction is proposed in the above noted Japanese Utility Model Laid-Open No. 115853/1987 wherein a part flow from of an exhaust air flow from a side of an electric driven blower receiving chamber is bypassed through a part of the inner wall portion of the vacuum cleaner main body. Namely this inner wall portion of the vacuum cleaner main body is positioned between the electric driven blower receiving chamber and an exhaust air flow passage adjacent the electric driven blower receiving chamber.
However, in the vacuum cleaner having the resonance type silencer mechanism comprising the sound absorption box, the exhaust air flow from the side of the electric driven blower receiving chamber is exhausted into a comparatively large space portion in the vacuum cleaner main body via a plurality of exhaust air ports provided on the sound absorption box.
By this conventional vacuum cleaner structure, the exhaust air noise reduction effect which is a feature of the resonance type silencer mechanism can be attained, in other words the reduction of the exhaust air noise level at a particular frequency band can be attained.
However, in case of the exhaust air noise occurring in the vacuum cleaner main body, from the results of a frequency analysis, the peaks of the frequency of the exhaust air noise exist at a plurality of the frequency numbers in many cases. Therefore, the exhaust air noise reduction effect in the vacuum cleaner main body cannot be obtained sufficiently because of the vacuum cleaner having the resonance type silencer mechanism.
Further, the electric driven blower used in the vacuum cleaner adopts a commutator motor as a driving means for the blower and the rotational speed of the commutator motor varies in accordance with the variation of the load.
More particularly, at the initial condition in the cleaning operation of the vacuum cleaner in which the dust does not be suctioned into the vacuum cleaner main body, the rotational speed of the commutator motor is low and, generally in the range of 20,000-27,000 rpm. When the dust is suctioned into the vacuum cleaner main body, the ventilation resistance in the vacuum cleaner main body increases so that the rotational speed of the commutator motor generally is in the range of 28,000-36,000 rpm.
Accordingly, the frequency number of the rotative vibrating exhaust air noise in accordance with the rotational speed of the commutator motor is variable. In the vacuum cleaner having the resonance type silencer mechanism, since only the exhaust air noise level at the particular frequency band can be reduced, the exhaust air noise reduction effect in the vacuum cleaner main body lowers the effectiveness of the vacuum cleaner.
Besides, in the conventional vacuum cleaner having the resonance type silencer mechanism structure, the vacuum cleaner adopts a structure in which a part flow of an exhaust air flow from the side of an electric driven blower receiving chamber, is bypassed through a portion of an inner wall of the vacuum cleaner main body. In other words, this inner wall portion of the vacuum cleaner main body is positioned between the electric driven blower receiving chamber and the exhaust air flow passage adjacent the electric driven blower receiving chamber.
In the above stated vacuum cleaner having the resonance type silencer mechanism structure, the exhaust air flow is not directly exhausted to the outside from the side of the electric driven blower receiving chamber, since the partial flow of the exhaust air flow is bypassed, the sound energy is converted to the heat energy during the passing through the exhaust air flow bypass passage in the vacuum cleaner main body.
Accordingly, an exhaust air noise reduction effect in the vacuum cleaner main body at some degree may be expected. However, in the above stated conventional vacuum cleaner having the resonance type silencer mechanism structure, since the length of the exhaust air flow passage is merely lengthened, the exhaust air noise passing through the vacuum cleaner main body remains large, therefore there has a room for improving from the aspect of the vacuum cleaner structure in which a sufficient silencing effect for the exhaust air in the vacuum cleaner main body can be obtained.